Apart from the fact that is just more hyperbole.
1st, by problem I meant actual issue like in the 1D MkIII. 2nd, even the very best avian raptor in flight specialists say there is no more than a 5% difference in keeper rate between the best AF currently available for that speciality and the 1DX MkII, and even that difference is predicated on a specific shooting style with both systems having different advantages.
I would have said (indeed I have been) a 5% difference makes the various systems comparable, not one 'a problem'. Now I can understand the very best of the best deciding that a 5% difference for their particular specialty is a significant enough benefit for them to change system. However I have no time or inclination for the vast majority of sheep who bleat endlessly when they don't have 1/10 the skill of those at the very top hiding behind idiot comments like 'the AF has a problem' because a rarified few have found the limits of the various AF algorithms, especially when there are instances of high profile high speed nature shooters who have gone the other way.
So now we have proven the A9/II, 1DX MkII and D5 have comparable iso performance
LINK, and that the best of the best who are also genuinely analytical about their AF rate the differences in keepers at around 5% for any of the top three I'd say the AF was also comparable.
To be sure I can understand why any individual might find one of the top three advantageous for their specific subjects and personal use, however I find the suggestion that any one of the three has 'a problem' or lags seriously behind any of the others as proof of only one issue and that issue is 6" behind the viewfinder.
I am no Canon apologist I am a photographer, give me a 1DX MKII, a D5 or an A9 and I'll take the same images, if I don't get the image the problem is me and you won't find me blaming any of the gear.